1. Field of the Invention
The present invention relates to a chemical mechanical polishing (to be referred to as xe2x80x9cCMPxe2x80x9d hereinafter) apparatus and a CMP method for pressing a wafer against a polishing pad with the wafer supported by a carrier, rotating the polishing pad to revolve the wafer about the center of the polishing pad relative to the polishing pad, rotating the wafer around its own central axis and thereby allowing the polishing pad to polish the wafer. The present invention particularly relates to a CMP apparatus and a CMP method capable of polishing a film formed on a wafer to be have a quite planarized surface.
2. Description of the Related Art
FIG. 1 shows the outline of a conventional CMP apparatus. A polishing pad 1 is driven to rotate about a central shaft 1a of the pad 1 and a backing plate 2 serving as a carrier is provided above the polishing pad 1. A carrier film 3 is bonded to the lower surface of the backing plate 2 and a wafer 4 is attached and fixed onto the lower surface of the backing plate 2 through the carrier film 3.
While the backing plate 2 is driven to rotate to thereby cause the wafer 4 to rotate on its own axis, a polishing target film 5 on the surface of the wafer 4 is pressed against the polishing pad 1, the wafer 4 is relatively revolved about the center of the polishing pad 1 by the rotation of the polishing pad 1 and the polishing target film 5 of the wafer 4 is thereby polished by the polishing pad 1. It is noted that the conventional backing plate 2 has a flat surface.
In the conventional CMP apparatus, however, it has been difficult to planarize the entire surface of the wafer uniformly and accurately. In recent years, planarity of about 30 nm (allowable irregularity) is demanded if the surface of a film, in which an embedded wiring such as damascene wiring is formed, is planarized. If this high planarity is not attained, erosion or recess which is a parameter indicating an depression amount at the time of forming, for example, a damascene wiring grows and the irregularity of wiring resistance thereby increases, then the reliability and acceleration of a circuit formed on the surface of the wafer is adversely affected.
Further, according to the conventional CMP technique, if irregularity exists in the radial direction of the wafer and the film thickness distribution of the polishing target film is concentric, they can be planarized. However, if irregularity exists in the circumferential direction of the wafer, they cannot be planarized by means of CMP.
Moreover, if a polishing apparatus has its own particularity as to the planarity of the polished surface of the wafer, the conventional CMP technique cannot eliminate the particularity.
Meanwhile, there is disclosed a method of adjusting the polishing pad of a CMP apparatus by dividing the pad surface of the polishing pad according to the film thickness distribution of the device surface of a semiconductor substrate and adjusting the surface roughness of the pad surface to have different roughnesses using a plurality of grindstones having different hardnesses (Japanese Patent Application Laid-Open No. Hei 10-180618). This is, however, a method for adjusting the surface roughness of the polishing pad and not for directly planarizing the wafer surface. The method is, therefore, not enough to apply to the high accuracy planarization of a wafer surface.
It is, therefore, an object of the present invention to provide a CMP apparatus and a CMP method capable of accurately, uniformly planarizing the polished surface of a polishing target film formed on a wafer throughout the wafer and capable of accurately planarizing the polishing target surface throughout the wafer even if irregularity exists in the circumferential direction of the wafer or a polishing apparatus has its own peculiarity in polishing.
A chemical mechanical polishing apparatus according to the present invention comprises a polishing pad; a carrier supporting a wafer as a polishing target; driving means for causing the carrier to rotate on its own central axis and revolving the carrier about a center of the polishing pad; and pressing means for pressing the wafer against the polishing pad through the carrier. To adjust contact pressure for contacting a polished surface of a polishing target film on the wafer with the polishing pad according to heights of the polished surface, it is preferable that a surface of the carrier is worked to have a high region corresponding to a high region of the polished surface of the polishing target film and to have a low region corresponding to a low region of the polished surface. Also, a film may be provided on a surface of the carrier, said film having a thick region corresponding to a high region of the polished surface of the polishing target film and having a thin region corresponding to a low region of the polished surface. A film may be provided on a surface of the carrier, said film having a hard region corresponding to a high region of the polished surface of the polishing target film and having a soft region corresponding to a low region of the polished surface. In this case, a difference in the height of the surface of the carrier is preferably 100 to 500 times as large as a difference in the height of the polished surface of the polishing target film. A plurality of pins protruding from a wafer support surface of the carrier and pin height adjusting unit for adjusting protruding heights of the pins may be provided.
Further, another chemical mechanical polishing apparatus according to the present invention comprises a polishing pad; a carrier supporting a wafer as a polishing target; driving unit for causing the carrier to rotate on its own central axis and rotating the carrier about a center of the polishing pad; and pressing unit for pressing the wafer against the polishing pad through the carrier, wherein contact pressure for contacting a polished surface of a polishing target film on the wafer with the polishing pad is adjusted depending on whether a region of the polished surface is polished easily or less easily based on a relationship between the carrier and the polishing pad.
In the above-stated chemical mechanical polishing apparatus, the adjusting means can be an adjusting means having in addition, the carrier is a stainless steel backing plate.
A chemical mechanical polishing method according to the present invention comprises the steps of pressing a wafer as polishing target against a polishing pad while the wafer is supported by a carrier; and rotating the polishing pad to rotate the wafer about a center of the polishing pad and to cause the wafer to rotate on its own central axis, is characterized by comprising the step of adjusting contact pressure for contacting a surface of the wafer with the polishing pad in accordance with heights of a surface of the wafer.
Another chemical mechanical polishing method according to the present invention comprises the steps of pressing a wafer as polishing target against a polishing pad while the wafer is supported by a carrier; and
rotating the polishing pad to rotate the wafer about a center of the polishing pad and to cause the wafer to rotate on its own central axis, is characterized by comprising the step of adjusting contact pressure for contacting a polished surface of a polishing target film on the wafer with the polishing pad depending on whether a region of the polishing target surface is polished easily or less easily based on a relationship between the carrier and the polishing pad.